I. Field of the Invention
The present invention relates generally to valve assemblies and, more particularly, to a valve assembly for use with a fuel tank.
II. Description of the Prior Art
Governmental regulations are becoming increasingly strict regarding the amount of hydrocarbons that can be emitted into the atmosphere from automotive vehicles. Such governmental regulations regulate not only the amount of hydrocarbons that can be exhausted from the automotive vehicle in the exhaust stream, but also hydrocarbons that enter into the atmosphere through leaks or other openings in the fuel system.
One major source of hydrocarbon pollutants that enter into the atmosphere from automotive vehicles results from fumes that escape from the fuel tank. Previously, many fuel tanks have been simply freely vented to the atmosphere which allows the automotive fuel fumes to freely and continuously enter the atmosphere.
In order to prevent the continuous venting of fuel fumes from the fuel tank, there have been previously known valve assemblies associated with the gas tank. These previously known valve assemblies operate to close the fill neck passageway except when the tank is filled with fuel. Consequently, the fuel vapors are vented to the atmosphere only when the fuel tank is filled with fuel.
With these previously known valve assemblies, however, it is also necessary to vent the fumes from the gas tank during the filling operation. In order to accomplish this, these previously known gas tank valve assemblies typically include two valves, a fuel valve which opens to permit fuel to enter into the tank during the filling operation, and a vent valve which opens to permit fumes to exhaust from the gas tank simultaneously with the entry of fuel.
One problem with these previously known gas tank valve assemblies is that the fuel and vent valves must not only operate in unison with each other, but must also firmly and sealingly close in all cases except during a filling operation. However, due to manufacturing tolerances, thermal expansion and the like, in many cases the vent valve and fill valve do not sealingly close in unison and with each other. When this occurs, leaks past either the fuel valve or the vent valve allow hydrocarbon vapors from the fuel tank to escape into the atmosphere.